This invention relates to liners for securely holding a workpiece centered in a machine tool and, more particularly, to a unibody liner for securing a workpiece in the hollow spindle of a turning machine for effectively controlling bar whip and its related problems.
Virtually all metal turning machine tools involve the feeding of bar or tube stock, which is commonly longer than the finished part upon completion of the machining process. Typically, the stock or workpiece is fed through a tubular spindle in the head stock of the machine to a chuck mechanism where the cutting operation occurs. The workpiece is secured by a chuck mechanism during the machining process while the entire length of the workpiece rotates. This rotation is typically at a high rate of revolutions per minute. As a workpiece is finished, a new workpiece is continually fed by an automatic or manual bar pusher rod mechanism.
When stock smaller than the inside diameter of the spindle is fed through the spindle and is clamped by the chuck mechanism while the entire bar is spinning, the stock remaining inside the spindle will rotate out of concentric rotation (e.g., wobble). This condition, commonly referred to as xe2x80x9cwhip,xe2x80x9d results in undesirable machine noise, unacceptable machined part tolerances, poor machine finishes, and vibration or xe2x80x9cchatter,xe2x80x9d which reduces the operator""s ability to predict or control the machining operation. Such conditions adversely effect the cutting or quality of the operation, often resulting in stock loss.
To address this condition and to improve machine performance, particularly at higher revolution speeds, xe2x80x9clinersxe2x80x9d were developed to fit in the through-opening of the spindle of the turning machine. Such a liner has a tubular shape with an axial opening extending along its entirety. The workpiece then fits through the axial opening of the liner. The liner has an outer diameter equal to part of the inner diameter of the spindle and an inner diameter slightly greater than that of the outside diameter of the bar stock, in order to concentrically fill the annular space between the workpiece and the inner wall of the spindle. Typically, a cylindrical filler tube or spindle liner for each size of the bar stock was used.
One conventional approach for reducing stock whip in the spindle of a turning machine is a cylindrical reduction tube constructed from metal to form the inside diameter, with a series of annular bearing rings or O-rings to establish the outside diameter. The inside diameter of the reduction tube is typically slightly greater than the outside diameter of the stock for the purpose of concentrically filing or reducing the space between the stock and the spindle, that is, the outside diameter of the reduction tube or liner is roughly equal to the inside diameter of the spindle.
In the use of the aforementioned prior art liner, a particular liner is selected from a set of spindle liners depending on the workpiece to be machined. The liner is inserted into the lathe and secured by way of a mounting flange disposed adjacent to one end of the liner and a set of fasteners (i.e., bolts) securing the liner to the turning machine. When a different sized workpiece is to be machined, the liner must be unfastened and removed to allow the next liner to be positioned and secured within the spindle.
Other prior art liners include those developed by Austin, U.S. Pat. No. 4,058,036; Winberg et al., U.S. Pat. No. 4,149,437; Spooner, U.S. Pat. Nos. 4,788,895 and 4,930,381; and Berns et al., U.S. Pat. No. 5,649,460. All of the aforementioned prior art devices suffer from being complex in design and expensive to manufacture.
This conventional method of filling the void between stock and the spindle still experiences various problems. First, the metal material of the spindle inner may not allow for feeding of non-uniform or slightly bowed bar stock. Second, when running hex, square, or extruded shaped bar stock, the inner bore of the conventional spindle liner does not take the shape of this stock through its entire length. Utilizing machined pins or dowel rings, the bar stock is only held at few locations (typically 2 or 3) and, therefore, control of the bar as it is fed through the machine is not fully optimized. Third, the metal-to-metal contact between the work piece and the interior of the metal liner has a tendency to mar or scratch the workpiece. Fourth, the metal-to-metal contact in a conventional spindle liner does not fully minimize vibration and the subsequent noise and control problems. This problem can lead to the requirement of several metal spindle liners for multiple bar stock sizes in close size proximity, which becomes expensive. It also can lead to the operator""s inability to fully control and optimize the productivity of the machine""s cutting operation.
In addition, in some cases the weight of the conventional metal spindle liner adds a significant amount of weight to the spindle, increasing the amount of turning mass, which in turn results in additional wear on the machine and the spindle. A conventional metal liner is also corrosive and, over time, will leave amounts of dirt and grime within the interior of the spindle. This adds to cost of maintaining and operating the metal turning machine.
Other concerns include the conventional spindle liner being easily damaged when not in use if dropped or impacted with any moderate degree of force. Finally, the conventional spindle liner requires complex machining and manufacture, which adds to the expense and lead time of conventional liners.
The present invention, provides a method and article involving a one-piece, unibody spindle liner formed from urethane material and having a tubular shape with an outside diameter and inside diameter that may be sized to fit virtually any spindle and to readily allow for the feeding therethrough of any size or shape of bar or tube stock.
This invention particularly relates to hollow liners utilized in a wide number of today""s machining operations for handling and feeding tubular or bar stock such that the axial centerline of the workpiece is maintained in concentric axial alignment with the working centerline of the turning machine. The liner of this invention may be configured as needed to accommodate workpieces of different sizes and shapes. Heretofore, it was commonly considered prohibitively expensive to provide multiple spindle liners for a large number of bar stock sizes and shapes. This invention eliminates that obstacle by providing a method of forming a one-piece liner that is considerably less expense than conventional liners, thereby enabling an operator of a turning machine to indeed have multiple liners on hand to accommodate the many varying sizes and shapes of bar or tube stock.
Through a molding process, the outside diameter of the unibody liner is sized to fit the dimensions of virtually any size spindle. The liner""s inner bore and diameter is molded to match and allow for feeding of virtually any size and shape stock being turned, including but not limited to round, hex, square, and extruded. Furthermore, the inner bore is molded into the spindle liner along its entire length providing absolute support of the workpiece. The spindle liner has a flanged mounting end to allow for proper orientation and attachment to the spindle.
This invention also presents a method of forming a unibody liner for a lathe spindle, including providing a mold for forming the unibody liner having an axial core piece that defines the through-opening of the liner. The core is intended to closely match the dimension of the workpiece to be machined. The mold includes an upper cap having a fill hole and a center locator pin that, in conjunction with a central pin disposed at the opposite end of the mold, secures and maintains the core piece in concentric alignment with the central axis of the mold. The poured polyurethane typically sets up within 15-30 minutes, after which time the molded liner is removed from the mold and placed in an oven for approximately 8-10 hours at 150 degrees F to complete the curing process. Thus, once the operator receives an order for a liner of specific dimensions, the liner mold may be configured to match the outer diameter and through-opening specifications, the urethane material poured in its liquid or molten state into the mold, the cured liner may then, after about 15-30 minutes, be removed from the mold, baked in a curing oven for about 8-10 hours, and then shipped to the customer, all within a single working day if necessary.
Such a one-piece, unibody liner provides many advantages over conventional metal spindle liners. The liner of this invention is considerably lighter in weight than metal liners. The reduced weight translates into less rotating mass within the spindle, thus lowering wear on the spindle and the turning machine. Another advantage is that the inner bore of the spindle liner of this invention can be molded to the shape and size of any stock being fed through the spindle. The bore for non-round stock is molded into the entire liner as opposed to just a few locations in the conventional metal liners. This allows for optimal control of bar whip and its associated problems.
In the conventional liner, a non-round work piece is not held or secured at all points along the entire length of the liner; it is held at only 2 or 3 locations along its length by pins or dowel rings. Consequently, as the non-round workpiece is being indexed, i.e., pushed/pulled, through the spindle during the cutting process, there""s a greater chance that the workpiece will rotate out of concentric center, thereby producing whip.
Furthermore, the spindle liner consists of, preferably, polyurethane material which has significantly higher vibration dampening or reduction properties than the metal material in conventional spindle liners. The liner provides the ability to hold proper part tolerances, thereby reducing scrap rates and increasing productivity. The bar stock is also protected from marring or scratching by the liner. The liner also reduces the wear on machine cutting tools due to the vibration deadening properties of the material from which it is constructed. Noise is also considerably reduced by the use of this novel liner. The machining operation is also able to be operated at a faster turning speed, while maintaining optimal machine control, thereby leading to improved productivity.
Multiple sizes or slightly bowed bar stock may be run in the same spindle liner because of the mechanical integrity and properties of the polyurethane material. The one-piece polyurethane spindle liner is also more durable and virtually indestructible as compared to the conventional metal spindle liner. It is also non-corrosive. Finally, the one-piece liner cost considerably less (upward to 50% less) to manufacture then the current industry standard metal liner.
This invention also provides a method of forming the one-piece polyurethane spindle liner that allows for significantly shorter delivery or lead times than the current industry standard for conventional metal spindle liners. Once the spindle inside diameter(s) is established for a specific machine make, a mold can be created to establish the spindle liner outside diameter. The only variable that remains is the shape and size of the inside diameter of the throughbore of the spindle liner. The mold core determines the cross-section of the spindle liner and can easily be changed as needed. Once the machine tool spindle inner dimension is known and the mold is established, the lead time can be as short as the same day to within a couple of days from the receipt of the order.
To overcome the above problems and shortcomings of the prior art, it is an object of the present indication to provide a bar stock support to minimize whipping and other undesirable radial or lateral motion of the bar stock while in the spindle during machining. Another object is to provide an inexpensive spindle liner that is simple to manufacture, thereby enabling an operator to have one or more of the liners of this invention readily on hand to accommodate workpieces of varying diameter and cross-sectional shapes.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.